The present invention relates to an amplifier that can be set to a high output power dynamic range and has a virtually constant added power efficiency.
It relates more particularly to producing a solid state power amplifier for microwave signals, in particular for satellite transmitters, adapted to operate in a frequency range close to 30 GHz, for example, and including a particular number of active components feeding a common load in parallel through an adapter consisting of a microcircuit made up of propagation lines, capacitors or inductors.
However, the invention relates equally to producing amplifier circuits with redundant amplifier stages in which the amplifiers are not necessarily power amplifiers.
Producing a solid state power amplifier using a two-state combiner employing microwave lines with an electrical length of λ/4, where λ is the wavelength of the signal to be amplified, is known in the art. This circuit combines the signals supplied by four active components and provides as a result of the combination two output power levels with a constant added power ratio according to whether one active component is turned on or four active components are turned on.
This circuit has the drawback that it can provide only two power levels, a maximum output power level and an output power level 6 dB lower. Apart from this, the lack of symmetry of the circuit means that it is not possible for any active component to operate in isolation.
Another prior art embodiment known as a Doherty amplifier, differing from the above embodiment that is based on using the number of active components to implement power control, controls the dynamic range of the output power by varying the load conductances of the active components as a function of the input power.
This type of amplifier has the drawbacks of combining only two active components and of being ill-suited to applications requiring redundancy.
Obtaining an added power efficiency that is weakly dependent on the output power to adapt the bias points of the active components to the output power is also known in the art. This solution is difficult to put into practice, however, and the dynamic range of the output power is limited.